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Previous Selection: Sam Warburton, Justin Tipuric, Stephen Ferris, Chris Robshaw
This position will raise the most debate among fans. There are a host of stars battling it out for the four or five spots on the plane.
As previously discussed, the breakdown will be a key battleground this summer and finding some form openside's to challenge the mighty David Pocock.
Sam Warburton was seen by many as a certainty to tour and a leading candidate to captain the side. His star has dimmed in the last 12 months but he is still a very strong candidate. He went toe-to-toe with David Pocock and Richie McCaw in November and more than held his own.
He will have to watch his back though as Justin Tipuric is flying at present. Rob Howley even considered the possibility of switching Warburton to the blindside to accommodate the rising star.
Wales' second-row injury list meant Howley drafted Aaron Shingler and his line-out presence into the test team, leaving Tipuric consigned to the bench.
There is also the outside chance that Dan Lydiate finds his feet quicker than expected and makes a late push to travel.
Ireland's Stephen Ferris is another player who was in flying form last season but the injury curse has struck again, leading some to doubt if he will come back as strong as before. He feels like he can, and he has proved the doubters wrong before.
He will take inspiration from Sean O'Brien who came back from hip surgery and quickly returned to his barnstorming best. Peter O'Mahony is another who could make a late push but he would probably have to rely on injury to make the plane.
Another who is on the road to recovery is the dynamic Tom Croft. A favourite of the Sky Sports gang, I doubt whether his all-round game is good enough compared to his rivals. He is easing himself back after a serious neck injury and will take time to find form.
He will struggle to break into an England backrow that is bursting at the seams. Chris Robshaw is an inspirational figure and this, combined with his graft and skill, could help him fill a role in the squad. Alongside him, there is the likes of Tom Woods, Calum Clark and Tom Johnson.
Johnson would appear the least likely given his limitations size-wise. Clark is just back after a lengthy suspension and will need to prove he has his temper in check. Woods is a player who doesn't get much credit but does mountains of unseen work.
Kelly Brown is having a huge season for Saracens and has just been named the Scottish captain. Gatland will appreciate his work-rate and ability at the breakdown.
There is also the option that Gatland will go for with four flankers given the problems at lock and rely on the versatility of the four flankers chosen.
Not considered due to injury: Dan Lydiate (March); Stephen Ferris (March); Calum Clark (March); Ross Rennie (uncertain).
Tourists: O'Brien, Tipuric, Warburton, Robshaw